Device for transforming direct current into alternating current or vice versa



p 1948- P. N. BENDIXEN 2,449,048

DEVICE FOR TRANSFQRIING DIRECT CURRENT INTO ALTERNATING CURRENT 0R VICE VERSA Filed Feb. a, 1946 Jrgg,

1 111-13- INVENTOR PALLE N/as fi'ND/X! ATTO R N EYS Patented Sept. 14, 1948 DEVICE FOR TRAN SFORMING DIRECT CUR- RENT INTO ALTERNATING CURRENT OR VICE VERSA Palle Niels Bendixen, Copenhagen, Denmark Application February 8, 1946, Serial No. 646,387 In Denmark February 18, 1944 3 Claims. 1

This invention relates to devices for transforming direct current into alternating current or vice versa, said device having a vibrating member alternatlngly connected with one or the other of two fixed contacts or sets of contacts.

In the devices of this type hitherto known, the vibrating member is provided with an armature attracted by an electro-magnet, the magnetizing coil of which is connected with a magnetizing switch adapted to be closed and opened through the vibrations of the armature, said armature thus acting as a self-braking automatic switch.

In such devices, a certain energy is .required for maintaining the vibrating movements of the vibrating member, which energy is not made otherwise useful, and the efficiency of the device will, consequently, be rather small, especially at small loads. Further, the period of vibration is, in such devices, limited by the mass and rigidness of the vibrating member, and is thus unable to surpass a certain limit.

The invention has for its object to provide a device of the type referred to, in which these inconveniences are avoided, i. e. a device permitting of transformation of direct current int alternating current at high efllciency, even at small loads. and permitting of a very much shorter period of vibration than heretofore.

Accordin to the invention, this object is obtained through the use of a piezo-electric crystal in the manner hereinafter set forth The invention will now be more fully described with references to the drawings in which Fig. 1 schematically shows a piezo-electric crystal element for use in a device according to the invention, for explaining the operation of the crystal element,

Fig. 2 shows one form of a device according to the invention, and

Fig. 3 shows a modified form of the device.

The crystal element shown in Fig. 1 may consist of seignette salt, for example. The crystal element comprises two crystal plates a and b, between which is disposed an electrode 3. On the sides of the crystal plates a and b remote from each other electrodes l and 2 are disposed which are connected together. As indicated in Fig. 1, the intermediate electrode 3 is connected with the positive terminal of a voltage source, whereas the outer electrodes l and 2 are connected with the negative terminal of said voltage source. Thus the outer electrodes will be negative, and thecrystal element will bend as exaggeratedly shown in full lines.

By reversing the polarity of the voltage source,

2 the outer electrodes will be positive, and the crystal element will bend in the opposite direction, such as indicated in dotted lines.

The fact is made use of in the device shown in Fig. 2. The crystal element, which is clamped between two blocks, is provided with a member l4 adapted to cooperate with two fixed contacts l6 and I8 and connected with the intermediate electrode 3. At its end remote from this member the crystal is rigidly clamped between the clamping blocks I0 and I2. The fixed contacts l6 and I8 are each connected with one terminal of a voltage source 20, the middle 22 of which is connected through a switch 24 with the outer electrodes I and 2 and with the primary winding 25 of a transformer connected in parallel with a condenser 30 to the intermediate electrode 3, the secondary winding of said transformer being connected with a consuming circuit.

The device described operates as follows:

When the switch 24 is closed,a current will flow through the transformer winding 26, the intermediate electrode 3, the member I4 and the fixed contact It to the negative pole of the voltage source 20. Hereby the electrodes of the crystal element are subjected to a direct voltage, the crystal element thereby bending itself so as to move the member I4 to contact with the fixed contact l8. Now the direction of current is reversed, the current iiowing from the positive pole of the battery over the contact l8,'the member 14, the intermediate electrode 3 and the transformer winding to the middle 22 of the battery. Hereby an opposed polarity is imposed on the electrodes the crystal element thereby bending itself back to the contact IS. The direction of current in the transformer winding 26 being, thus, constantly reversed during the vibrations of the crystal element, an alternating voltage will be induced in the secondary winding 28 of said transformer.

The form shown in Fig. 3 difiers from that shown in Fig. 2 in the outer electrodes I and 2 and the intermediate electrode ,3, respectively, being each connected with one end of the secondary winding 28 of the transformer.

Further, the contact member M of the crystal element is isolatedly fixed to the crystal element by means of an insulating layer 32, and the voltage source 20 is inserted between the contact member l4 and the middle point of the primary winding 26.

The device operates as follows:

, When the switch 24 is closed, a current will flow through one half part of the transformer winding 26 thereby inducing an opposed current in the secondary winding 28 which will cause the crystal element to bend itself to switch over the contact member H. The further operation is like that described with reference to Fig. 2.

It will be understood that other modes of wiring are possible within the scope of the ap pended claims, it being only necessary that an alternating polarity is imposed on the electrodes of the crystal element during the vibrations of the same.

Even if the device in the foregoing is described as adapted to transform direct current into alternating current, it will be understood that it is also capable of performing the reversed operation.

WhatIclaim is:

1. A device of the kind referred to, comprising a pair of opposed contacts, a contact member for alternatingly co-operating with said contacts, a piezo-electric crystal element composed of a pair of crystal members connected together, said crystal element carrying said contact member, an intermediate electrode disposed between said crystal members, outer electrodes disposed on the outer faces of said crystal members, and means controlled by said contact member and pair of contacts for imposing alternating voltage on said intermediate electrode and said outer electrodes.

2. A device of the kind referred to,,comprising a pair of opposed contacts, connected with opposed ends of a direct voltage source, a contact member for alternatingly co-operating with said contacts, a piezo-electric crystal element composed of a pair of crystal members and carrying said contact member, an intermediate electrode disposed between said crystal members and electrodes disposed on the outer faces of said crystal element and connected with an intermediate point of said voltage source, and a transformer, the primary coil of said transformer being connected at one end with said intermediate point of the voltage source and at the other end with said intermediate electrode.

3. A device of the kind referred to, comprising a pair of contact members connected with 0pposed ends of the primary coil of a transformer, a contact member for alternatingly co-operating with said contacts and connected with one end of a direct voltage source, said voltage source being connected at its other end with an intermediate point of said primary coil, a piezo-elec' tric crystal element composed of a pair of crystal members and isolatedly carrying said contact member, an intermediate electrode disposed between said crystal members and connected with one end of the secondary coil of said transformer, and outer electrodes disposed on the outer faces of said crystal element and connected with the other end of said secondary coil.

PALLE NIELS BENDIXEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,450,246 Cady Apr. 3, 1923 1,919,053 Brinton July 18, 1933 2,235,317 Gibbs Mar, 18, 1941 

